package LianXi;

import java.util.Scanner;

public class L7 {
	
	public static void main(String[] args) {
		Scanner input=new Scanner(System.in);
		int sum=0;
		for(int i=1;i<=100;i++) {
			if(i%2!=0) {
				sum+=i;
			}
		}
		System.out.println(sum);
	}

}
